use empty_index_set for serialize empty index (antgroup#429)

Signed-off-by: LHT129 <tianlan.lht@antgroup.com>

Author: LHT129

src/algorithm/hgraph.cpp

@@ -22,26 +22,12 @@
 
 #include "common.h"
 #include "data_cell/sparse_graph_datacell.h"
+#include "empty_index_binary_set.h"
 #include "impl/pruning_strategy.h"
 #include "index/hgraph_index_zparameters.h"
 #include "logger.h"
 
 namespace vsag {
-static BinarySet
-empty_binaryset() {
-    const std::string empty_str = "EMPTY_INDEX";
-    size_t num_bytes = empty_str.length();
-    std::shared_ptr<int8_t[]> bin(new int8_t[num_bytes]);
-    memcpy(bin.get(), empty_str.c_str(), empty_str.length());
-    Binary b{
-        .data = bin,
-        .size = num_bytes,
-    };
-    BinarySet bs;
-    bs.Set(BLANK_INDEX, b);
-
-    return bs;
-}
 
 static uint64_t
 next_multiple_of_power_of_two(uint64_t x, uint64_t n) {
@@ -252,7 +238,7 @@ HGraph::EstimateMemory(uint64_t num_elements) const {
 tl::expected<BinarySet, Error>
 HGraph::Serialize() const {
     if (GetNumElements() == 0) {
-        return empty_binaryset();
+        return EmptyIndexBinarySet::Make("EMPTY_HGRAPH");
     }
     SlowTaskTimer t("hgraph Serialize");
     size_t num_bytes = this->cal_serialize_size();

src/empty_index_binary_set.h

@@ -0,0 +1,43 @@
+
+// Copyright 2024-present the vsag project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#pragma once
+
+#include <cstring>
+
+#include "vsag/binaryset.h"
+#include "vsag/constants.h"
+
+namespace vsag {
+class EmptyIndexBinarySet {
+public:
+    static BinarySet
+    Make(const std::string& name = "EMPTY_INDEX") {
+        const std::string empty_str = name;
+        size_t num_bytes = empty_str.length();
+        std::shared_ptr<int8_t[]> bin(new int8_t[num_bytes]);
+        memcpy(bin.get(), empty_str.c_str(), empty_str.length());
+        Binary b{
+            .data = bin,
+            .size = num_bytes,
+        };
+        BinarySet bs;
+        bs.Set(BLANK_INDEX, b);
+
+        return bs;
+    }
+};
+
+}  // namespace vsag

src/index/diskann.cpp

@@ -28,6 +28,7 @@
 #include <utility>
 
 #include "data_cell/flatten_datacell.h"
+#include "empty_index_binary_set.h"
 #include "impl/odescent_graph_builder.h"
 #include "io/memory_io_parameter.h"
 #include "quantization/fp32_quantizer_parameter.h"
@@ -619,29 +620,11 @@ DiskANN::range_search(const DatasetPtr& query,
     }
 }
 
-BinarySet
-DiskANN::empty_binaryset() {
-    // version 0 pairs:
-    // - hnsw_blank: b"EMPTY_DISKANN"
-    const std::string empty_str = "EMPTY_DISKANN";
-    size_t num_bytes = empty_str.length();
-    std::shared_ptr<int8_t[]> bin(new int8_t[num_bytes]);
-    memcpy(bin.get(), empty_str.c_str(), empty_str.length());
-    Binary b{
-        .data = bin,
-        .size = num_bytes,
-    };
-    BinarySet bs;
-    bs.Set(BLANK_INDEX, b);
-
-    return bs;
-}
-
 tl::expected<BinarySet, Error>
 DiskANN::serialize() const {
     if (status_ == IndexStatus::EMPTY) {
         // return a special binaryset means empty
-        return empty_binaryset();
+        return EmptyIndexBinarySet::Make("EMPTY_DISKANN");
     }
 
     SlowTaskTimer t("diskann serialize");

src/index/diskann.h

@@ -205,9 +205,6 @@ class DiskANN : public Index {
     tl::expected<void, Error>
     load_disk_index(const BinarySet& binary_set);
 
-    static BinarySet
-    empty_binaryset();
-
 private:
     std::shared_ptr<LocalFileReader> reader_;
     std::shared_ptr<diskann::PQFlashIndex<float, int64_t>> index_;

src/index/hnsw.cpp

@@ -27,6 +27,7 @@
 #include "common.h"
 #include "data_cell/flatten_datacell.h"
 #include "data_cell/graph_datacell_parameter.h"
+#include "empty_index_binary_set.h"
 #include "index/hnsw_zparameters.h"
 #include "io/memory_block_io_parameter.h"
 #include "io/memory_io_parameter.h"
@@ -421,29 +422,11 @@ HNSW::range_search(const DatasetPtr& query,
     }
 }
 
-BinarySet
-HNSW::empty_binaryset() {
-    // version 0 pairs:
-    // - hnsw_blank: b"EMPTY_HNSW"
-    const std::string empty_str = "EMPTY_HNSW";
-    size_t num_bytes = empty_str.length();
-    std::shared_ptr<int8_t[]> bin(new int8_t[num_bytes]);
-    memcpy(bin.get(), empty_str.c_str(), empty_str.length());
-    Binary b{
-        .data = bin,
-        .size = num_bytes,
-    };
-    BinarySet bs;
-    bs.Set(BLANK_INDEX, b);
-
-    return bs;
-}
-
 tl::expected<BinarySet, Error>
 HNSW::serialize() const {
     if (GetNumElements() == 0) {
         // return a special binaryset means empty
-        return empty_binaryset();
+        return EmptyIndexBinarySet::Make("EMPTY_HNSW");
     }
 
     SlowTaskTimer t("hnsw serialize");

src/index/hnsw.h

@@ -319,9 +319,6 @@ class HNSW : public Index {
     tl::expected<void, Error>
     merge(const std::vector<MergeUnit>& merge_units);
 
-    static BinarySet
-    empty_binaryset();
-
     void
     init_feature_list();
 

src/index/pyramid.cpp

@@ -16,25 +16,11 @@
 #include "pyramid.h"
 
 #include "data_cell/flatten_interface.h"
+#include "empty_index_binary_set.h"
 #include "impl/odescent_graph_builder.h"
 #include "io/memory_io_parameter.h"
-namespace vsag {
-
-static BinarySet
-empty_binaryset() {
-    const std::string empty_str = "EMPTY_INDEX";
-    size_t num_bytes = empty_str.length();
-    std::shared_ptr<int8_t[]> bin(new int8_t[num_bytes]);
-    memcpy(bin.get(), empty_str.c_str(), empty_str.length());
-    Binary b{
-        .data = bin,
-        .size = num_bytes,
-    };
-    BinarySet bs;
-    bs.Set(BLANK_INDEX, b);
 
-    return bs;
-}
+namespace vsag {
 
 std::vector<std::string>
 split(const std::string& str, char delimiter) {
@@ -346,7 +332,7 @@ Pyramid::search_impl(const DatasetPtr& query, int64_t limit, const SearchFunc& s
 tl::expected<BinarySet, Error>
 Pyramid::Serialize() const {
     if (GetNumElements() == 0) {
-        return empty_binaryset();
+        return EmptyIndexBinarySet::Make("EMPTY_PYRAMID");
     }
     SlowTaskTimer t("Pyramid Serialize");
     size_t num_bytes = this->cal_serialize_size();